1. Field of the Invention
The present invention relates to a new transition metal compound, a catalyst for olefin polymerization containing this transition metal compound and a method for producing a propylene/ethylene-α-olefin block copolymer using this catalyst for olefin polymerization, more particularly relates to a new transition metal compound constituting a catalyst for olefin polymerization in a metallocene type catalyst, that is, a new transition metal compound, which can form the metallocene type catalyst that has well-balanced reactivity between ethylene and a comonomer selected from α-olefins having 3 to 20 carbon atoms and produces an α-olefin polymer (hereinafter, may be referred to as CP) of a high molecular weight, and a catalyst for olefin polymerization containing this transition metal compound, and a method for producing a propylene/ethylene-α-olefin block copolymer using this catalyst for olefin polymerization.
2. Description of the Prior Art
A polypropylene based resin material is broadly used and is given important post as an industrial material because of its many excellent performance mainly such as moldability, various properties, economical efficiency and environmental issues adaptability.
A polypropylene based resin material is so important in industrial fields that further improvement of its performance has been ever pursued in many aspects. In order to improve its flexibility and impact resistance, for example, a method for adding an elastomer such as ethylene-propylene rubber to a propylene homopolymer or a method for producing a so-called block copolymer by multistage polymerization where propylene and ethylene are copolymerized subsequently after homopolymerization of propylene, have been carried out.
While such a polypropylene based resin material is industrially produced mainly with a conventional Ziegler-Natta type catalyst and a metallocene type catalyst, there are many problems to be solved therein.
For example, a propylene based block copolymer obtained by polymerization in the presence of a conventional Ziegler-Natta type catalyst necessarily contains a low molecular weight component (oligomer component etc.), due to the catalyst properties, which not only causes generation of smoke and malodor during processing, but also poses various problems such as bad odor effect and deterioration of antiblocking property due to sticking even after processing.
In contrast, it has been known for a long time that highly isotactic polypropylene can be obtained by polymerizing propylene using a metallocene type catalyst different from a conventional Ziegler-Natta type catalyst. It is also disclosed that a so-called block copolymer is produced by multistage polymerization (see, for example, Patent Document 1), and further, a propylene-ethylene block copolymer having high stiffness and impact resistance is produced using a metallocene type catalyst (see, for example, Patent Documents 2 and 3).
Although a metallocene type catalyst is characterized by having generally higher polymerization activity compared with a conventional Ziegler-Natta type catalyst and providing a polymer having a narrow molecular weight distribution and a uniform distribution of copolymer compositions, it has still many problems to be solved such as a economical problem due to use of a metallocene compound to be synthesized in a complicated process and use of MAO as well as necessity for improving polymerization activity, molecular weight and stereoregularity of a polymer.
And, various researches for improving a metallocene type catalyst have been continued from various standpoints, for example, a transition metal compound that provides polypropylene having a high melting point is disclosed in order to improve stiffness of a propylene-ethylene block copolymer (see, for example, Patent Documents 4 and 5), however, there is a problem that the reactivity of ethylene is lower compared with that of propylene when propylene and ethylene are copolymerized using a catalyst composed of these transition metal compounds. In other words, it is necessary to polymerize with feeding a gas of a much deviated monomer ratio from the content in a copolymer in order to obtain the copolymer having a desired content of ethylene, it has a problem on producing, further, a copolymer having a desired content can not sometimes be produced in an extreme case.
Although it has been shown that the reactivity of propylene and the reactivity of ethylene can be changed by changing a transition metal compound to be used (see, for example, Patent Document 6 and Non-patent Document 1), transition metal compound that fills sufficient balance of the reactivity of both compounds has not been known so far, and especially when copolymerization of propylene and ethylene is carried out in a gas phase, transition metal compound that fills the reactivity of both compounds with sufficient balance has not been known so far.
In addition, for example, it is necessary for a propylene-ethylene block copolymer to show a low glass transition temperature in order to attain a high impact resistance, it is preferable that the content of each of propylene and ethylene in the copolymer satisfies the specific range in order to satisfy this (see, for example, Non-patent Document 2). Therefore, as the property of catalyst in production, it is necessary that the reactivity of propylene and the reactivity of ethylene has a good balance and is in a specific range respectively.
Further, when a known transition metal compound is used, it poses a problem that the obtained copolymer has a low molecular weight in the case of gas phase copolymerization of propylene and ethylene. In order to attain high impact resistance in a propylene-ethylene block copolymer, it is necessary for a molecular weight of copolymer to have a value over a specific level, and thus a transition metal compound and a catalyst that can produce a copolymer having a higher molecular weight are desired.
Still more, in order to improve impact resistance of polypropylene, it is also disclosed the improvement of impact resistance by blending ethylene-higher α-olefin rubber (the α-olefin has 4 to 8 carbon atoms) (see, for example, Patent Documents 7 and 8).
Such a rubber copolymer, however, has a shape difficult to handle depending on its composition and causes troubles in blending operation such as a trouble that it can not be pelletized unlike a crystalline resin. In the case of so-called polymer blending, wherein a rubber copolymer is added to polypropylene, the rubber copolymer is not dispersed sufficiently, which makes it difficult to attain high stiffness and impact resistance at the same time.
A method for producing an ethylene-higher α-olefin rubber such as an ethylene-butene rubber (EBR) and an ethylene-octene rubber (EOR) in multistage polymerization is also known. For example, a method for producing a propylene/ethylene-α-olefin block copolymer excellent in stiffness and impact resistance by carrying out multistage polymerization using a metallocene catalyst is disclosed (see, for example, Patent Documents 9 to 11).
Liquid-phase polymerization using a solvent, however, has a problem that efficient production is difficult because a formed CP dissolves in the solvent resulting in necessity for the solvent to be distilled off in order to separate the polymer.
Gas phase polymerization for producing a CP portion by using a specific transition metal compound is also disclosed (see, for example, Patent Documents 12 to 15).
A method using these specific transition metal compounds, however, has a problem that a CP having a sufficiently high molecular weight can not be produced in the industrially feasible range of temperature/pressure.
While stiffness and impact resistance have been improved to a certain extent by the above disclosed inventions, there is still a room for improvement in the molecular weight and the comonomer composition of an ethylene-α-olefin copolymer providing higher impact resistance. A method for stably and efficiently producing a propylene/ethylene-α-olefin block copolymer containing the copolymer that can satisfy the above properties has been desired to be developed.
In view of the above described background arts, a metallocene type polymerization catalyst, which is important and essential for the industrial production of a polypropylene based resin material broadly and conveniently used in many industrial fields has still many problems therein. One important problem among the above problems is that the reactivity of ethylene and the reactivity of an α-olefin having 3 to 20 carbon atoms do not balance in the copolymerization of the ethylene and the α-olefin having 3 to 20 carbon atoms resulting in difficulty in obtaining high molecular weight. An object of the present invention intends to solve such problems and to develop a metallocene type catalyst for α-olefin polymerization that shows balanced reactivity of ethylene and an α-olefin having 3 to 20 carbon atoms and gives a copolymer of a high molecular weight.    Patent Document 1: JP-A-4-337308    Patent Document 2: JP-A-11-228648    Patent Document 3: JP-A-11-240929    Patent Document 4: JP-A-11-240909    Patent Document 5: JP-A-2000-95791    Patent Document 6: WO2004-87775    Patent Document 7: JP-A-6-192500    Patent Document 8: JP-A-6-192506    Patent Document 9: JP-A-9-316145    Patent Document 10: JP-A-9-316147    Patent Document 11: JP-A-10-158351    Patent Document 12: WO95-27740    Patent Document 13: WO2005-23890    Patent Document 14: WO2005-23891    Patent Document 15: WO2005-23892    Patent Document 16: JP-A-10-226712    Patent Document 17: JP-A-2003-292700    Patent Document 18: JP-A-2004-002310    Patent Document 19: JP-A-2004-155739    Patent Document 20: JP-A-60-130604    Patent Document 21: JP-A-4-100808    Patent Document 22: JP-A-3-234709    Patent Document 23: JP-A-5-247128    Non-patent Document 1: Journal of the American Chemical Society 2001, vol. 123, p. 9555.    Non-patent Document 2: Polymer 2001, vol. 42, p. 9611.